A numerical model to predict fiber tow saturation during liquid composite molding

A dual scale porous medium contains two distinct scales of pores. We will consider the case in which small scale pores are ordered within well-defined sub-regions. Typical examples of such media are textile preforms used in various composite-manufacturing processes. Rigorously, the phenomenon can be modeled by using Darcyʹs law to describe flow through porous medium and mass conservation for the flow within the larger pores. The smaller pores can be included within these equations as a sink term. This approach, though straightforward, poses implementation difficulties. In this paper, we suggest an alternative way to model this concept. We use the standard finite element/control volume approach and model the “internal” sink term by appending extra one-dimensional elements to control volumes associated with the control volumes of discretized part geometry. This approach offers two advantages over previously attempted schemes: (1) the problem to be solved remains linear and flow can be calculated explicitly within the time domain and (2) existing simulation packages for RTM filling simulation will be able to incorporate saturation effects to simulate the flow in dual scale media. To illustrate this point we present the implementation of the developed algorithm within the frameworks of an existing simulation package LIMS. The implementation is capable of providing saturation data during filling of arbitrarily shaped part and can capture the influence of saturation on filling pressure or flow-rate. This should prove useful in determining the time needed to completely saturate the fiber tows, which is crucial for part performance and also allow us to explain the variation in injection pressure and difficulties in “assigning” single scale permeability for such porous medium.